For thirty years, predictive genetic tests ("capable of informing a healthy person at the time of the test whether or not he/she will become ill") have been offered to children with one parent suffering from a genetic disease such as Huntingdon's disease. Although the outcome was uncertain in the past with children with one sick parent having a one in two chance of developing the condition , the test should now "distinguish between those who will develop the disease and those who will be spared". Before offering such tests, doctors wondered whether the individuals concerned would undergo the test available to them? How would they react to the test result? Contrary to their predictions, however, "the facts suggest that most individuals respond in an essentially counter-intuitive fashion".
On the one hand, a result confirming the presence of the defective gene "will generally be accepted" whereas "things are far from straightforward" for those who thought they were carriers only to find out that they are not. On the other hand, although initial inquiries indicated that, "approximately 70% of individuals at risk agreed to take the test as soon as it became available", in reality, only 15% actually did so.
Individuals who do not have the test think: "What's the point if you can't change anything?". This state of mind has also been "corroborated by data recorded for other diseases, showing that diagnostic tests are carried out more frequently when there are real chances of treatment". As for the 15% who are tested for an incurable disease, "they want to rule out any uncertainty" and "do not want to pass on defective genes to their offspring". However, this second reason cannot be justified in the case of a prenatal genetic test: "In couples expecting a child where one of the parents has an incurable disease, such tests are used to less of an extent than tests for adults at risk of genetic disease. Most parents choose to have a child who, at the time of their birth, is at risk of one day developing the same condition as them".
This fact was proven in a French study carried out in 2016. Out of 54 couples enrolled in the study, "45% will conceive a baby naturally, without having the prenatal test". For others, prenatal screening of the condition will mostly lead to abortion . Some still choose pre-implantation screening whilst others have to give up any hopes of having a child. For Alexandra Dürr, team geneticist, "the desire to have a child is the overriding factor". In addition, "prenatal tests can be traumatic, especially if they lead to therapeutic abortion and, according to the geneticist, it's a procedure that no couple takes lightly". Finally, in a second study pending publication, "thirteen couples wanted to find out about prenatal testing but, before undergoing the test, they confirmed that they would have an abortion in the event of an unfavourable result". In reality, no-one reacted in this way. Prenatal screening followed by abortion has not eliminated the condition as scientists "had hoped".
Faced with a vast number of genetic tests on offer, many prefer not to know their risks. Patients' reactions challenge the predictions of the scientists.
 Huntington's disease is caused by gene mutation. A child who inherits a copy of the defective gene will develop the condition.
 "Doctors have no right to oblige women to have an abortion but international guidelines are strongly in favour of this to prevent the child from undergoing a masked predictive test. In this case, the child's status would be known regardless of whether or not the child would want to know on reaching adulthood, or know without telling anyone else"
Slate, Laura Spinney (04/10/2017)